package blockchain

import (
	"fmt"
	"github.com/p9c/p9/pkg/block"
	"math"
	"runtime"
	
	"github.com/p9c/p9/pkg/qu"
	
	"github.com/p9c/p9/pkg/hardfork"
	"github.com/p9c/p9/pkg/txscript"
	"github.com/p9c/p9/pkg/util"
	"github.com/p9c/p9/pkg/wire"
)

// txValidateItem holds a transaction along with which input to validate.
type txValidateItem struct {
	txInIndex int
	txIn      *wire.TxIn
	tx        *util.Tx
	sigHashes *txscript.TxSigHashes
}

// txValidator provides a type which asynchronously validates transaction inputs. It provides several channels for
// communication and a processing function that is intended to be in run multiple goroutines.
type txValidator struct {
	validateChan chan *txValidateItem
	quitChan     qu.C
	resultChan   chan error
	utxoView     *UtxoViewpoint
	flags        txscript.ScriptFlags
	sigCache     *txscript.SigCache
	hashCache    *txscript.HashCache
}

// sendResult sends the result of a script pair validation on the internal result channel while respecting the quit
// channel.
//
// This allows orderly shutdown when the validation process is aborted early due to a validation error in one of the
// other goroutines.
func (v *txValidator) sendResult(result error) {
	select {
	case v.resultChan <- result:
	case <-v.quitChan.Wait():
	}
}

// validateHandler consumes items to validate from the internal validate channel and returns the result of the
// validation on the internal result channel. It must be run as a goroutine.
func (v *txValidator) validateHandler() {
out:
	for {
		select {
		case txVI := <-v.validateChan:
			// Ensure the referenced input utxo is available.
			txIn := txVI.txIn
			utxo := v.utxoView.LookupEntry(txIn.PreviousOutPoint)
			if utxo == nil {
				str := fmt.Sprintf(
					"unable to find unspent "+
						"output %v referenced from "+
						"transaction %s:%d",
					txIn.PreviousOutPoint, txVI.tx.Hash(),
					txVI.txInIndex,
				)
				var e RuleError
				e = ruleError(ErrMissingTxOut, str)
				v.sendResult(e)
				break out
			}
			// Create a new script engine for the script pair.
			sigScript := txIn.SignatureScript
			// witness := txIn.Witness
			pkScript := utxo.PkScript()
			inputAmount := utxo.Amount()
			vm, e := txscript.NewEngine(
				pkScript, txVI.tx.MsgTx(),
				txVI.txInIndex, v.flags, v.sigCache, txVI.sigHashes,
				inputAmount,
			)
			if e != nil {
				str := fmt.Sprintf(
					"failed to parse input "+
						"%s:%d which references output %v - "+
						"%v (input witness x, input script "+
						"bytes %x, prev output script bytes %x)",
					txVI.tx.Hash(), txVI.txInIndex,
					txIn.PreviousOutPoint, e, // witness,
					sigScript, pkScript,
				)
				e = ruleError(ErrScriptMalformed, str)
				v.sendResult(e)
				break out
			}
			// Execute the script pair.
			if e := vm.Execute(); E.Chk(e) {
				str := fmt.Sprintf(
					"failed to validate input "+
						"%s:%d which references output %v - "+
						"%v (input witness x, input script "+
						"bytes %x, prev output script bytes %x)",
					txVI.tx.Hash(), txVI.txInIndex,
					txIn.PreviousOutPoint, e, // witness,
					sigScript, pkScript,
				)
				e = ruleError(ErrScriptValidation, str)
				v.sendResult(e)
				break out
			}
			// Validation succeeded.
			v.sendResult(nil)
		case <-v.quitChan.Wait():
			break out
		}
	}
}

// Validate validates the scripts for all of the passed transaction inputs using multiple goroutines.
func (v *txValidator) Validate(items []*txValidateItem) (e error) {
	if len(items) == 0 {
		return nil
	}
	// Limit the number of goroutines to do script validation based on the number of processor cores.
	//
	// This helps ensure the system stays reasonably responsive under heavy load.
	maxGoRoutines := runtime.NumCPU() * 3
	if maxGoRoutines <= 0 {
		maxGoRoutines = 1
	}
	if maxGoRoutines > len(items)*3 {
		maxGoRoutines = len(items) * 3
	}
	// maxGoRoutines = 1
	//
	// Start up validation handlers that are used to asynchronously validate each transaction input.
	//
	// TODO: this creates an insane amount of goroutines that run for tens of milliseconds each and... well... parallelize...
	for i := 0; i < maxGoRoutines; i++ {
		go v.validateHandler()
	}
	// Validate each of the inputs.
	//
	// The quit channel is closed when any errors occur so all processing goroutines exit regardless of which input had
	// the validation error.
	numInputs := len(items)
	currentItem := 0
	processedItems := 0
	for processedItems < numInputs {
		// Only send items while there are still items that need to be processed. The select statement will never select
		// a nil channel.
		validateChan := make(chan *txValidateItem)
		var item *txValidateItem
		if currentItem < numInputs {
			validateChan = v.validateChan
			item = items[currentItem]
		}
		select {
		case validateChan <- item:
			currentItem++
		case e := <-v.resultChan:
			processedItems++
			if e != nil {
				v.quitChan.Q()
				return e
			}
		}
	}
	v.quitChan.Q()
	return nil
}

// newTxValidator returns a new instance of txValidator to be used for validating transaction scripts asynchronously.
func newTxValidator(
	utxoView *UtxoViewpoint, flags txscript.ScriptFlags,
	sigCache *txscript.SigCache, hashCache *txscript.HashCache,
) *txValidator {
	return &txValidator{
		validateChan: make(chan *txValidateItem),
		quitChan:     qu.T(),
		resultChan:   make(chan error),
		utxoView:     utxoView,
		sigCache:     sigCache,
		hashCache:    hashCache,
		flags:        flags,
	}
}

// ValidateTransactionScripts validates the scripts for the passed transaction using multiple goroutines.
func ValidateTransactionScripts(
	b *BlockChain, tx *util.Tx, utxoView *UtxoViewpoint, flags txscript.ScriptFlags, sigCache *txscript.SigCache,
	hashCache *txscript.HashCache,
) (e error) {
	// // First determine if segwit is active according to the scriptFlags. If it isn't then we don't need to interact with
	// // the HashCache.
	// segwitActive := flags&txscript.ScriptVerifyWitness == txscript.ScriptVerifyWitness
	// // If the hashcache doesn't yet has the sighash midstate for this transaction, then we'll compute them now so we can
	// // re-use them amongst all worker validation goroutines.
	// if segwitActive && tx.MsgTx().HasWitness() &&
	// 	!hashCache.ContainsHashes(tx.Hash()) {
	// 	hashCache.AddSigHashes(tx.MsgTx())
	// }
	var cachedHashes *txscript.TxSigHashes
	// if segwitActive && tx.MsgTx().HasWitness() {
	// 	// The same pointer to the transaction's sighash midstate will be re -used amongst all validation goroutines. By
	// 	// pre-computing the sighash here instead of during validation, we ensure the sighashes are only computed once.
	// 	cachedHashes, _ = hashCache.GetSigHashes(tx.Hash())
	// }
	if ContainsBlacklisted(b, tx, hardfork.Blacklist) {
		return ruleError(ErrBlacklisted, "transaction contains blacklisted address ")
	}
	// Collect all of the transaction inputs and required information for
	// validation.
	txIns := tx.MsgTx().TxIn
	txValItems := make([]*txValidateItem, 0, len(txIns))
	for txInIdx, txIn := range txIns {
		// Skip coinbases.
		if txIn.PreviousOutPoint.Index == math.MaxUint32 {
			continue
		}
		txVI := &txValidateItem{
			txInIndex: txInIdx,
			txIn:      txIn,
			tx:        tx,
			sigHashes: cachedHashes,
		}
		txValItems = append(txValItems, txVI)
	}
	// Validate all of the inputs.
	validator := newTxValidator(utxoView, flags, sigCache, hashCache)
	return validator.Validate(txValItems)
}

// checkBlockScripts executes and validates the scripts for all transactions in
// the passed block using multiple goroutines.
func checkBlockScripts(
	block *block.Block, utxoView *UtxoViewpoint,
	scriptFlags txscript.ScriptFlags, sigCache *txscript.SigCache,
	hashCache *txscript.HashCache,
) (e error) {
	// // First determine if segwit is active according to the scriptFlags. If it isn't
	// // then we don't need to interact with the HashCache.
	// segwitActive := scriptFlags&txscript.ScriptVerifyWitness == txscript.ScriptVerifyWitness
	// Collect all of the transaction inputs and required information for validation
	// for all transactions in the block into a single slice.
	numInputs := 0
	for _, tx := range block.Transactions() {
		numInputs += len(tx.MsgTx().TxIn)
	}
	txValItems := make([]*txValidateItem, 0, numInputs)
	for _, tx := range block.Transactions() {
		// hash := tx.Hash()
		// If the HashCache is present, and it doesn't yet contain the partial sighashes for this transaction, then we
		// add the sighashes for the transaction. This allows us to take advantage of the potential speed savings due to
		// the new digest algorithm (BIP0143).
		// if segwitActive && tx.HasWitness() && hashCache != nil &&
		// 	!hashCache.ContainsHashes(hash) {
		// 	hashCache.AddSigHashes(tx.MsgTx())
		// }
		var cachedHashes *txscript.TxSigHashes
		// if segwitActive && tx.HasWitness() {
		// 	if hashCache != nil {
		// 		cachedHashes, _ = hashCache.GetSigHashes(hash)
		// 	} else {
		// 		cachedHashes = txscript.NewTxSigHashes(tx.MsgTx())
		// 	}
		// }
		for txInIdx, txIn := range tx.MsgTx().TxIn {
			// Skip coinbases.
			if txIn.PreviousOutPoint.Index == math.MaxUint32 {
				continue
			}
			txVI := &txValidateItem{
				txInIndex: txInIdx,
				txIn:      txIn,
				tx:        tx,
				sigHashes: cachedHashes,
			}
			txValItems = append(txValItems, txVI)
		}
	}
	// Validate all of the inputs.
	validator := newTxValidator(utxoView, scriptFlags, sigCache, hashCache)
	// start := time.Now()
	if e = validator.Validate(txValItems); E.Chk(e) {
		return e
	}
	// elapsed := time.Since(start)
	// Tracec(func() string {
	//	return fmt.Sprintf("block %v took %v to verify", block.Hash(), elapsed)
	// })
	//
	// // If the HashCache is present, once we have validated the block, we no longer need the cached hashes for these
	// // transactions, so we purge them from the cache.
	// if segwitActive && hashCache != nil {
	// 	for _, tx := range block.Transactions() {
	// 		if tx.MsgTx().HasWitness() {
	// 			hashCache.PurgeSigHashes(tx.Hash())
	// 		}
	// 	}
	// }
	return nil
}